There is a need in many industries for a simple apparatus and process to separate or concentrate a first phase relative to a second phase in a two phase flowing fluid. Such commercial and industrial applications for the present invention occur in the fields of medicine, food manufacturing, energy, electronics, imaging devices, chemicals, ceramics, and many others.
In one embodiment, for example, this invention relates to a liquid dispersion filtration and delivery processes in the manufacturing or fabrication of products in which effective filtration is required in order to ensure the quality of end products, for example, the manufacturing or fabrication and coating of thin films such as photoconductors, photographic film, and magnetic films. In particular, one embodiment of the invention relates to a high precision, high purity micro-filtered coating dispersion filtration and delivery apparatus including a crossflow filtration device in close proximity to a coating operation.
Photoconductive members or photoreceptors, that are for example organic, and which are used in electrophotographic machines, are well known. In the manufacture or fabrication of organic photoreceptors or the like, an organic solvent, a binder resin, and a pigment can be combined and milled for use in a charge generation layer thereof. The pigment and binder resin are chosen to optimize their photoconductive properties, but it is not always possible to optimize the dispersion quality of the resulting coating fluid. Charge generating dispersions that become unstable over time are a common problem in the fabrication of certain organic photoreceptors. Unstable dispersions and particulate impurities result in coating defects in the charge generating layer that lower coating yield during the fabrication process.
Current known photoreceptor coating dispersions containing pigments such as, e.g. benzimidazole perylene and hydroxygallium phthalocyanine, flocculate extensively when quiescent or when handled at low shear flow conditions. Reference may had to U.S. Pat. No. 6,195,443 of Hammond, the disclosure of which is incorporated herein by reference. Further reference may be had to the paper, “A Novel Technique for Investigation of Flow Behavior of Flocculating Dispersions,” J. Hammond et al, presented at the International Coating Science and Technology Symposium, Wilmington, Del., May 1998, the disclosure of which is incorporated herein by reference.
Conventional filters in which all of the coating fluid entering the filter housing passes through the filter element typically operate at low shear near the surface of the filter medium. Thus, when a highly flocculating dispersion is delivered into a conventional filter device by a conventional delivery system, flocs of pigment ordinarily tend to form near the surface of the filter medium. The flow field moves the flocs onto the surface and into the bulk of the filter medium, ultimately resulting in plugging of the filter. In photoreceptor manufacturing or similar film or web coating operations, a plugged filter may cause a significant amount of downtime for a filter change, including restart and stabilization of the coating process (for example, for the purging of air bubbles from the filter device). This is obviously a costly interruption of such manufacturing process.
In one coating process embodiment, an initial countermeasure to such a filter problem was simply to use a filter element with a 40 micron pore size. Such a pore size was large enough that the pigment flocs, which form near the filter medium, did not plug the filter. Attempts to filter the dispersion using filter elements rated to retain particles small than 40 microns resulted in plugging of the filters with pigment flocs.
However, in embodiments of organic photoreceptor manufacturing, and other thin film device manufacturing, it is undesirable to use a filter that will allow the passage of particles in the 1 micron to 40 micron size range. Such particles and/or flocs may disrupt flow out of the extrusion die or other coating applicator, causing streaks. Also, the presence of particles of this large a size in the wet coated generator layer is known to result in defects in the dried generator layer. Both particles and streaks will show as defects in the final printed output to the end customer; therefore, any photoreceptor having such defects will not be acceptable.
The suggested use of a crossflow filter is an improvement over prior art filters. However, conventional coating fluid delivery systems in which such a filter is installed are ordinarily not optimum. They are often complex and do not locate the filter in close proximity to the coating die or other coating applicator. Therefore, such a conventional delivery system does not minimize the incidence of particulate defects and pigment flocs, which may be present in the coating fluid that is delivered into the die, and subsequently onto the coated film or photoreceptor. As such, the problem of filtering the coating dispersion at a process location immediately before and in close proximity to the coating application has not been addressed. Such a location of the filter significantly reduces the opportunity for the filtrate to be re-contaminated with undesired particles as it flows from the filter to the coating applicator. The use of a filter in very close proximity to the end use of the filtrate is known as “point-of-use” filtration in the semiconductor industry, and is a highly desired apparatus and process attribute.
There are numerous other applications for the apparatus and processes of the present invention. The present invention is not limited in any way solely to the production of a filtrate. Rather, the present invention is an apparatus and a process to separate or concentrate a first phase relative to a second phase in a multi-phase flowing fluid; or to separate or concentrate a first particle size population relative to a second particle size population in a multi-phase flowing fluid.
For example, in the manufacturing of a foodstuff such as a soup, the present invention may be used to perform a separation thereby providing a first highly viscous, stew-like product stream to a first destination, and a second less viscous broth-like product stream to a second destination. The present invention is further advantageous because it provides a filtration process wherein a high fluid shear rate exists at the surface of the filter medium. Such a process is useful in the preparation of shear-thinning foodstuffs, such as peanut butter. In one embodiment of the apparatus and process of the present invention, the present invention may be used to perform a separation of flowing peanut butter, wherein a first product stream comprises a “crunchy” peanut butter product comprising solid peanut chunks dispersed in liquid peanut butter flowing to a first destination, and a second product stream comprises a “creamy” liquid peanut butter flowing to a second destination. Many other similar uses of the present invention will be apparent to those skilled in the art.
In the preparation of abrasive particulate slurries used in e.g., surface cleaning, roughening, smoothing, and/or polishing, the present invention may be used to provide a first product stream comprising a population of large particles, and a second product stream comprising a population of small particles. Such a process may be used in the preparation of e.g., high precision optics. In the field of energy, such a use of the present invention has similar applicability in the preparation of coal-water slurries. In the field of mining, such a use of the present invention has similar applicability in the preparation of mineral or ore slurries prior to extraction or smelting.
In the semiconductor electronics industry, the present invention may be used to prepare a substantially particulate-free filtrate to be delivered to a filtrate-using destination, such as e.g., a wafer, magnetic storage disc, or compact disc spin-coating process. Such spin-coating operations are well known in the art of data disc manufacturing and semiconductor manufacturing.
The present invention is also widely applicability in biomedical devices, to separate or concentrate a first phase relative to a second phase in a flowing metabolic fluid; or to separate or concentrate a first particle size population relative to a second particle size population in a flowing metabolic fluid. In one embodiment, the apparatus of the present invention is miniaturized and integrated into a small implantable device, which may be used as e.g. an artificial organ performing a separation process. In another embodiment, the apparatus of the present invention is miniaturized and integrated into a small implantable device, which may be used as e.g. an device to deliver a drug comprising a material phase which would otherwise flocculate or congeal if not maintained in a flowing state at high shear.
It is an object of this invention to provide an apparatus and a method for producing a filtrate comprising fine particles in a liquid, in close proximity to a filtrate-using destination.
It is an object of this invention to provide an apparatus and a method for producing a filtrate comprising fine particles wherein the filter medium does not plug and become blocked by such particles.
It is an object of this invention to provide an apparatus and a method for producing a filtrate comprising fine particles, which is simple to construct.
It is an object of this invention to provide a method for producing a filtrate and a decantate, which is simple to operate and control.
It is an object of this invention to provide an apparatus and a method for producing a first fluid stream comprising large particles and a second fluid stream comprising small particles, wherein the filter medium does not plug and become blocked by such particles.
It is an object of this invention to provide an apparatus and a method for producing a filtrate comprising fine particles wherein the filter medium does not plug and become blocked by such particles, and wherein such apparatus is made sufficiently small as to be implantable within a human body.
It is an object of this invention to provide an apparatus and method for filtering and/or classifying a fluid containing magnetic particles.